1. Technical Field of the Invention
This invention relates to bismaleimides. More particularly, this invention relates to novel bismaleimide derivatives obtained from oxyethylene diamines and anhydrides. Still more particularly, this invention relates to novel bismaleimide derivatives prepared by reacting at least about 0.5 mole equivalents of di-, tri- or tetraethylene glycol diamines with maleic anhydride in a two-step process.
The bismaleimide monomers and prepolymers formed have improved solubility and processibility; the polymers they are used to prepare may be tougher and more flexible than other polybismaleimides.
They may be used alone as monomers to give homopolymers, or in combination with other materials such as aliphatic or aromatic diamines or unsaturated compounds including aromatic bismaleimides to give copolymers.
2. Prior Art
Bismaleimide polymers are important primarily for their thermal stability, which usually results from aromaticity in the structure. Although the majority of bismaleimides have therefore prepared from aromatic diamines, aliphatic compounds can also provide benefits in improved processibility, flexibility and solubility, Bismaleimides have, for example, been prepared from alkylene-diamines (J. Appl. Poly. Sci, 29, 891-899 (1984) and from JEFFAMINE.RTM. ED-diamines (U.S. Pat. No. 3,951,502). In a series of Japanese patents issued to Mitsui Toatsu Chemicals (JP 82 205,413; 83 40,374; 83 15,515; 83 136,637), bismaleimides were also prepared from diamines such as 4,7-dioxadecane-1,10diamine (reduction product of cyanoethylated ethylene glycol) and related diamines; these are used with polybutadiene in preparation of copolymers. The maleimide of triethylene glycol monoamine is also reported in one of these patents. Use of the oxyethylene group to increase flexibility has been effective in some other types of polymers as well. In J. Macromol. Sci.--Chem., A21, 1117-1135 (1984) there is described preparation of "reactive plasticizers" with acetylene endgroups and internal oxyethylene groups. Stenzenberger, in German Pat. No. 2,127,024 disclosed the preparation of an aliphatic bismaleimide from 2,2,4-trimethylhexane-1,6-diamine and in German Pat. No. 2,165,974 he described its thermal polymerization.
The use of mixtures of polyoxyalkylene bismaleimides (with molecular weights greater than 400) and aromatic bismaleimides in preparation of flexibilized polybismaleimides is disclosed by de Koning in European patent application No. 206,383. While the heat distortion temperature fell with increasing amounts of flexibilizing bismaleimide, the elongation and flexure at break both increased.
In U.S. Pat. No. 4,237,262, Jones discloses a low temperature curable composition comprising at least one curable polyimide prepolymer formed by heating an aliphatic oxyalkylene bismaleimide with an aromatic polyamine and at least one aromatic bismaleimide and at least one aliphatic epoxy resin. The reaction product provides at least two functional epoxy groups to provide a low temperature curable composition. In U.S. Pat. No. 3,951,902 Jones et al. discloses a compliant polyimide having superior thermal mechanical properties produced by reacting an aromatic bis(furfurylimide) with an aliphatic ether bis(maleimide) via a Diels-Alder reaction.
In U.S. Pat. No. 4,116,937, Jones also discloses a resin system prepared by Michael addition of a mixture of oxyalkylene and aromatic bismaleimides to aromatic diamines. The oxyalkylene bismaleimides have molecular weights of about 750, and the product is a glassy solid at room temperature.
In the work described in 4,116,937 the objective was to make elastomers. The elongations for the polymers described in the examples therein range from 70% to 170%. These polymers were probably not very rigid, this property being a function of the molecular weight of the amines used and the distance between maleimide units. Another disadvantage is that the amines used here are aromatic amines, which are in many cases known or suspected to be carcinogenic or otherwise toxic; although the tissue is not specifically addressed, it is not likely the "flexible polyimide precursor", with its aromatic content, would be soluble to any great extent in water.
Nagaski, in European patent application No. 191,931, reveals the use of certain oxyalkylene bismaleimides in rubber compositions.
A curable resin composition is disclosed in Jpn. Kokai Tokkyo Koho JP 58, 136,637 [83,136,637] 13 Aug. 1983 to Mitsui Toatsu Chemicals. The compound contains an aliphatic imide and polybutadiene containing double bonds.
A Japanese Patent to Mitsui Toatsu Chemicals, Inc. (JP 58,127,735 [83,127,735] (C1. C08G 73/10), 29 July 1983) discloses heat resistant electrical insulators for printed circuit boards which are prepared from mixtures of aliphatic polyether bisimides, aromatic bisimides and diamines.
An aritcle by White in Ind. Eng. Chem. Prod. Res. Dev. 25, 395-400 discusses the fact that bisimides offer potential for the synthesis of high-molecular-weight, step growth polymers. It is stated they are flanked by two electron-withdrawing carbonyl groups, and the electrophilic maleimide carbon-carbon-double bond is especially labile to nucleophilic attack and yields Michael type adducts with both amines and thiols. The paper focuses on the requirements for preparation of these polymeric Michael adducts, with additional emphasis on the effects of the enormous structural variety available within the class in thermal and physical properties of these new resins.
In the art experimental data are available wherein polymers were synthesized which are structurally related to those formed by nucleophilic or Michael addition of diaminoarenes, but which had more flexible backbones and lower glass transition temperature (Tg). See "Reaction of Diaminoalkanes with Bismaleimides: Synthesis of Some Unusual Polyimides", Journal of Applied Polymer Science, Vol. 29, 891-899 (1984).
Shaw and Kinloch have studied the effects of rubber concentration on the morphology, bulk mechanical and thermal properties and the adhesive strength of the bismaleimide by the addition of various amounts of a carbonyl-terminated butadiene (CTBN) rubber toughening agent, and concluded that surprisingly large amounts of CTBN rubber can be added to substantially improve the fracture resistance of the bismaleimide resin without sacrificing other important properties. (See "Toughened Bismaleimide Adhesives", Int. J. Adhesion, July 1985, pp. 123-127.)
A growing number of applications for polyimides are discussed in the an article titled "Premium Performance from Polyimides" in ME, January 1986, p. 14-19.
In U.S. Pat. No. 4,277,582 Mueller discloses water-insoluble hydrophilic copolymers consisting of a hydrophilic polymer of monoolefinic monomers cross-linked with a major amount of a diolefinic non-hydrophilic macromer.
It appears there is a large market for bismaleimides and a good deal of research in the art has been directed toward studying properties of and better methods for producing these compounds. Bismaleimide compounds are increasingly important in high performance polymers commonly used as matrix resins for composites. It is believed that polybismaleimide derivatives of the instant invention, particularly those derived from di-, tri- and tetraethylene glycol diamines including bisaminoethyl ether, JEFFAMINE.RTM. EDR-148 and JEFFAMINE.RTM. EDR-192 would be useful as monomers in homopolymers and copolymers and would exhibit advantages including improved flexibility, processibility, toughness and solubility. They could be used alone or in combination with other materials such as aliphatic or aromatic diamines or unsaturated compounds (including aromatic bismaleimides) to give copolymers.
The series of oxyethylene diamines consisting of BAEE (bisaminoethyl ether, or diethylene glycol diamine), JEFFAMINE.RTM. EDR-148 (triethylene glycol diamine), and JEFFAMINE.RTM. EDR-192 (tetraethylene glycol diamine) are promising candidates for conversion to bismaleimides (eqs. 1,2). Incorporation of bismaleimides made from these diamines could give new prepolymers and polymers with enhanced flexibility, processibility of solubility. The polymer prepared from the adduct of EDR-148 and EDR-148 BMI was a relatively hard material with a high flexural modulus (close to 500,000 psi). In the instant invention there was less distance between the maleimide units than in, for example, the case of 4,116,937, where the amines had a minimum molecular weight of 600, and therefore the instant polymers exhibited more rigidity. Another advantage of the instant invention is that the prepolymer products exhibit solubility in water unlike products resulting from the use of aromatic amines.
One derivative, in particular, is the bismaleimide of triethylene glycol diamine. This bismaleimide should be quite useful as a monomer, but it is solid. This detracts from its usefulness for many applications. By a method disclosed in a second embodiment of the instant invention it is converted to a liquid form suitable for polymerization. Water-soluble bismaleimides and polybismaleimides have been sought in recent years, and compounds such as the prepolymers of this invention could prove to be especially useful in this respect.